Underwater biotelemetry includes studies of movements, behavior, and physiological functions of underwater animals, as well as environmental conditions surrounding them. In such studies data are received via signals from a transmitter on or in an animal. Ultrasonic signals were used in early work. More recently both ultrasonic and radio signals have been used.In the two decades since the first underwater biotelemetry studies in the mid-1950s there have been considerable technical advances. Transmitters have become smaller, more powerful, and have longer operating life. Coding of individual transmitters has become more reliable and decoding more automated. Transmitters capable of sensing environmental, behavioral, and physiological factors from free-swimming animals have been built. Receiving systems ranging from small ones for tracking from canoes to large ones for oceangoing vessels have been developed.With this equipment about 60 species of underwater animals have been studied. Various techniques of transmitter attachment have been developed and different methods of tracking explored.Underwater biotelemetry has been applied to studies of fish migration, orientation mechanisms, movement patterns at obstructions, ecology, behavior, and physiology of animals. Key words: telemetry, underwater biotelemetry, tracking, sonic tags, transmitters, receivers, hydrophones

A radiotelemetry apparatus is described for sensing and transmitting electromyograms (EMGs) from free-swimming fish. EMGs are recorded from the epaxial muscles of adult rainbow trout during periods in spontaneous (= routine) activity, and forced-swim, respirometers. When such EMG records are integrated, subjected to spectral analysis, and computer-averaged, the EMG values (in pV) are highly correlated with the fish oxygen consumption during the activity periods. However, there is a marked difference between the regression slopes for oxygen v. EMG value for the data from the spontaneous, and forcedswim, respirometers; the former slope is the steeper. The probable explanation of this phenomenon is that whereas in forced swims the epaxial myomeres are responsible for most of the activity of the fish, in spontaneous activity other muscle systems ( e g of the lateral, dorsal and ventral fins) come to account for a greater relative proportion ofbody movement. The difference in slope, although great, is evidently a regular phenomenon. The shift from one regression to the other occurs at a fairly precise epaxial EMG value (c. 5 pV). This suggests that the laboratory calibration of EMG value in terms of oxygen consumption can be utilized in the wild so that EMG records from free-swimming fish, fitted with telemetry packages can be used to deduce oxygen consumption attributable to activity. It also appears that such records can be used as a guide to the type of activity of the fish, i.e. desultory movements or free cruising.

A new automated ultrasonic telemetry system for monitoring the swimming activity of adult rainbow trout, Sufmo gairdneri, at liberty in the wild is described. The transmitter detects bioelectric potentials (i.e. electromyograms) associated with the contraction of the epaxial myomeres during swimming. Transmitter output is relayed to the signal processing system via submerged hydrophones. The incoming signals represent averaged electromyograms which have been shown in earlier studies to correlate well with swimming activity and concurrent oxygen consumption of rainbow trout in the laboratory.Electromyogram records obtained from rainbow trout released into a small lake and monitored for up to 4 weeks, indicate a fairly regular pattern of elevated midday activity contrasting with periods of relative quiescence during the evening and morning. This midday peak in locomotory activity is the result of an increased feeding activity which is evidently a response to a concomitant increase in the activity of the fish's prey.

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A small transmitter (7 × 1.6 cm) for telemetering swimming depth of aquatic animals was developed. The transmitter operates for 3 days with a signal range of about 1 km in sea water. It codes depth to 40 m or more as changes in pulse repetition rates, detectable by standard ultrasonic receivers.